The present invention relates to the production of polycarbonate using a melt transesterification reaction between a diaryl carbonate and a dihydroxy compound. In the melt transesterification process, dihydroxy compounds such as bisphenol A are reacted with diaryl carbonates such as diphenyl carbonate (DPC) or more preferably with ester-substituted diaryl carbonates such as bismethylsalicylcarbonate (BMSC).
U.S. Pat. No. 4,323,668, which is incorporated herein by reference, describes a polycarbonate transesterification process comprising reacting an ester-substituted diaryl carbonate and a dihydric phenol in the presence of a catalyst under transesterification reaction conditions. In the specific examples, U.S. Pat. No. 4,323,668, which is incorporated herein by reference, makes uses of bismethylsalicylcarbonate (BMSC) as the diaryl carbonate. Use of ester-substituted diaryl carbonates in the production of polycarbonate is also described in U.S. Pat. No. 6,420,512, U.S. Pat. No. 6,506,871, U.S. Pat. No. 6,548,623, U.S. Pat. No. 6,790,929, U.S. Pat. No. 6,518,391, US Application Serial No. 2003/0139529, and US Application Serial No. 2003/0149223 all of which are incorporated herein by reference.
In these patents it is discussed that the use of ester-substituted diaryl carbonate as the carbonate source allows for increased transesterification rates, when compared to processes using DPC, and superior polymer properties. However, additional improvements are still desired. For example, water is often used as a solvent for melt transesterification catalysts including sodium hydroxide. In melt transesterification reactions using DPC this is not necessarily problematic in that water is an excellent solvent and does not adversely affect the performance of the DPC. It has herein been found, that although water is an excellent solvent for melt transesterification catalysts, water readily hydrolyzes ester-substituted diaryl carbonates thereby altering the molar ratio of reaction components within the melt polymerization reaction. Furthermore, other known solvents such as benzene and other carcinogenic solvents are not desirable because of their toxicity. Additionally water and other foreign materials added to the melt polymerization reaction will likely be present within the product polycarbonate.
It would be beneficial to find a method of introducing reaction components into reaction equipment without introducing foreign materials into the reaction equipment that would hinder the formation reaction and/or be present within the product polycarbonate or in the overhead stream of the phenolic byproduct of the transesterification reaction as it exits the equipment.